Electronics Wizzes - Help with Tracking down a buzzing in my headphones

Forums › Gadgets, robotics, home automation, electronics (including wearables) › Electronics Wizzes - Help with Tracking down a buzzing in my headphones

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richms

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#1066340 16-Jun-2014 00:01

networkn:
richms: Antenna being going to a home theater reciever, TV, etc that is connected to the same computer or DAC somehow, also USB cables carry a chassis ground so unplug any of those going off to external drives and printers etc that are powered seperatly.

Ok. I did all that already in the troubleshooting in my OP. I don't have any gear not listed, connected (Unless you are talking indirectly as in, on the same electrical circuit in the house).

With absolutly no input filtering or visible filtering on the AC from the transformer other than some large electorlytics which are useless for high frequancy noise, there is the real chance that you are just picking up RF noise which the circuitry is demodulating, and if it comes from something else on the earth wire from something else having a noisy switching power supply then it will come across as a buzz at mains frequancy normally.

The construction looks like a bad noisy 60 year old valve radio, so I wouldnt be expecting much more than that qualitywise from it.

Richard rich.ms

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Aredwood

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#1066343 16-Jun-2014 00:09

networkn:
Aredwood: The audio ground and the mains ground will be connected together inside the crack amp. And inside your PC. this means you have a loop that starts at the multi box or your houses earth wiring, runs to the case of your PC, through the ground wire in your audio cable to the crack amp. Out the crack amps power cable back to the multi box / house wiring. Using the laptop breaks the loop because Laptop power supplies even if they are 3 pin normally don't carry the ground connection through to the laptops chassis connection.

Try the ground loop isolator from trademe to verify that it is a ground loop problem. If you don't want to use it permanently. The best way (I think) is to modify the crack amp. What you need to do is have separate audio ground and mains ground. Connect the metal panels, Transformer case ect to the earth pin On the crack amp. Insulate the ground of the RCA connections and the headphone connections from the case if not done already. Make sure that no other audio grounds are connected to the case. Get a high current bridge rectifier such as http://jaycar.co.nz/productView.asp?ID=ZR1324&w=bridge+rectifier&form=KEYWORD Connect the +and - terminals together. And the 2 AC terminals together. Then connect 1 side to your audio ground. And the other side to the mains ground. This will block any small circulating currents because the diodes in the bridge rectifier will only start conducting if there is more than 0.5V difference. But if mains power somehow livens the audio ground, The diodes which can handle 70A (2X35A in parallel) will easily conduct it to ground so the circuit breaker / fuse will still cut the power as normal.

Thanks for the detailed reply. I sort of understand SOME of that. I am not sure I'd have the technical knowledge to undertake the modification to the crack amp, though it sounds like the best way to go, without idiot proof instructions, with pictures etc. I presume all these changes would then change the resistance and voltage checks, so I'd have no way of knowing what they should be.

I will send off your very useful suggestion to the manufacturer of the kits and see what they have to say.

I think I say you say you are a sparky by trade, is there an idiot proof (read safe) way to check that the "house" is grounded?

Also I'd want to ensure that any changes I made to the Crack Amp would not change it sonically.

I am sure your house will be grounded. The problem is that the combination of your houses mains cables, audio signal / usb cables, and equipment. means you have an earth wire that is connected in a circle. a small amount of electricity is flowing around that circle which is coupling into your signal cables. Therefore causing the noise.

The mains isolating transformer, the audio ground loop isolator, and my suggested modification to the crack amp. Are 3 different ways of achieving the same thing. Breaking that circle.

Thanks for the compliment about me being a sparky. I am actually a Plumber / Gasfitter by trade. But I do electronics as a hobby. Designing / building circuits, both audio and digital, Arduino based ect. Also building my own computers / networking, own automotive work - engine swaps including different engines from factory, EFI work ect, And lots of other technical things as well. If it is technical I like doing it. The electronics knowledge comes in very handy for diagnosing / fixing problems on modern gas appliances. Which often have extensive electronic controls. Infinity water heaters being the best example.

Have a read of some of the articles on http://sound.westhost.com/ There is a massive amount of information on that website. Most of it is related to audio circuits. And lots of projects again mostly related to audio. Im sure you will find it really interesting.

sir1963

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#1066368 16-Jun-2014 07:18

networkn: Well I won't be doing any more tonight. I just gave myself 240v through the chest trying to get a closer picture. Not sure what I was thinking etc. Not sure how it happened either a bit shaky. The RCD tripped and I dropped the crack amp so it's bent a few things, will require a full check over tomorrow. I don't recall touching both hands to the metal but I can't see any other way it could have happened. The power switch on the crack amp was turned off, but stupidly (though it didn't occur to me at the time), I had the power cable in.

My new suggestion, get someone to do this for you.
You obviously don't have the technical knowledge or skills to do this safely
I ask you as both a registered electrician and a electronics service engineer to get someone competent involved, this is NOT worth yours or someone else's life.

networkn

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#1066809 16-Jun-2014 17:02

richms: When you connect the cable to the PC, you are creating another ground loop. Also chances are the output devices on the DAC are not active when there is no signal coming into them.

What do you get if you have the DAC plugged into the PC but the PC is powered down or in sleep? Still get the noise?

Looking at the design of it I can see why they sell it as a kit - they would be sued out of existance in no time selling something that poorly made pre-built.

Well to be fair, it arrived as a component pack, so they are not responsible for how it turns out, and of course if they were assembling it and selling it, they would need all SORTS of extra protections.

I'll have to check the whole amp again probably tomorrow night now, and then I can test the PC sleeping if it causes the issue, but I removed everything except the Power and Toslink cable from the PC whilst it was on and still had the problem. I was told the ground loop couldn't exist under those conditions, but the hum/buzz was still present so
perhaps it's not a ground loop after all.

networkn

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#1066811 16-Jun-2014 17:07

richms:
networkn:
richms: Antenna being going to a home theater reciever, TV, etc that is connected to the same computer or DAC somehow, also USB cables carry a chassis ground so unplug any of those going off to external drives and printers etc that are powered seperatly.

Ok. I did all that already in the troubleshooting in my OP. I don't have any gear not listed, connected (Unless you are talking indirectly as in, on the same electrical circuit in the house).

With absolutly no input filtering or visible filtering on the AC from the transformer other than some large electorlytics which are useless for high frequancy noise, there is the real chance that you are just picking up RF noise which the circuitry is demodulating, and if it comes from something else on the earth wire from something else having a noisy switching power supply then it will come across as a buzz at mains frequancy normally.

The construction looks like a bad noisy 60 year old valve radio, so I wouldnt be expecting much more than that qualitywise from it.

It's a very well respected amp and hundreds or perhaps thousands of them are in existence, other than the buzz/hum I have, the amplification really make both headphones I have sing. I can't argue the technical side of it with you since this is a beginner project for me, but given the popularity of it, and the community, I'd be surprised if it was as bad as
you are suggesting. I am not intentionally arguing with you, I appreciate any assistance I can get from anyone.

networkn

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#1066812 16-Jun-2014 17:14

sir1963:
networkn: Well I won't be doing any more tonight. I just gave myself 240v through the chest trying to get a closer picture. Not sure what I was thinking etc. Not sure how it happened either a bit shaky. The RCD tripped and I dropped the crack amp so it's bent a few things, will require a full check over tomorrow. I don't recall touching both hands to the metal but I can't see any other way it could have happened. The power switch on the crack amp was turned off, but stupidly (though it didn't occur to me at the time), I had the power cable in.

My new suggestion, get someone to do this for you.
You obviously don't have the technical knowledge or skills to do this safely
I ask you as both a registered electrician and a electronics service engineer to get someone competent involved, this is NOT worth yours or someone else's life.

I am getting someone competent involved, there seems to be quite a number of people who seem to know a fair bit, contributing to this thread and the one on the forums for the Amp itself. I made a mistake in handling it, I accept that, and I certainly don't want to die doing it.

To pay someone to "fix" this, would probably cost a fortune and be more cost effective to throwit out and buying something premade, and I have greatly enjoyed building this.

I certainly learned a valuable lesson in this experience, one upon reflection I should have known better for, but as they say hindsight is 20/20.

Niel

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#1066849 16-Jun-2014 17:42

The term earth loop is a bit generic. What actually happens is that any signal even a few hundred hertz does not care that you have all equipment earthed. Instead the return path will be the loop with the smallest area. With a coax cable this is easy, as the signal wire is surrounded by the return shield. But it also means you get minute differences when different signals return via different earth connections and this is where you are getting noise. (Electronic product design engineer, and part time sound engineer both live and post processing.)

See how it goes with the ground loop isolator off TradeMe, it will most likely solve the issue and you will not notice the insertion loss.

The electrical shock does not require touching 2 wires, your feet is a return path. Your body has a resistance of about 500 Ohm and your skin has a breakdown voltage of around 120V so there can be a fair bit of resistance in the return path and you will still get shocked. Some countries do not have earth connected to earth for that reason.

Consider that the kit is sold overseas so likely not designed for NZ product safety requirements. Fine for home-build, but strictly speaking you should get someone to test it for appliance safety (essentially that all exposed metal is earthed and can handle significant fault current).

(If using an isolation transformer then the e.g. USB cable from the laptop will not cope with mains fault currents, neither will the EMC filters.)

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